A common step used during the assembly of active and passive devices onto a printed circuit board (PCB) is a wave solder step. Wave soldering devices onto the PCB provides an automated method of interconnecting leads on the devices to solder pads on the PCB.
Referring to FIG. 1, during a typical wave solder operation a pallet 10 receives at least one PCB 12, and is placed on a conveyor (not shown) which moves the PCB along the wave solder machine (not shown). The wave solder generally comprises three steps: A fluxer applies flux to the bottom side of the PCB to prepare or clean the solder pad surfaces so the solder will adhere, then the PCB is preheated. Finally, the PCB is moved to the solder wave for electrical connection of the leads on the devices to the solder pads on the PCB.
Problems which can result from wave soldering include the formation of shorts and shadowing. Shorts occur when solder bridges two adjacent solder pads, and shadowing occurs when a trailing solder pad is not supplied adequate solder due to the effect of another pad on the flow of the solder wave. With shadowing, a weak solder connection is formed on the trailing pad which can cause the PCB to fail during testing, or the PCB may pass testing but fail during use. An apparatus which reduces shorts and shadowing would be desirable.
U.S. Pat. No. 5,024,370, which is incorporated herein by reference, describes a wave solder apparatus.